MODULATION OF FLIGHT BY THE GIANT INTERNEURONS OF THE COCKROACH

In this paper, I have examined the behavioral functions of feedback lo ops between the cockroach (Periplaneta americana) giant interneurons ( GIs) and the flight thoracic rhythm generator. 1. During sequences of flight-like activity, I have recorded from identified giant interneuro ns from the dorsal (dGIs) or the ventral (vGIs) group and stimulated t hem either with current pulses or with wind stimuli delivered to the c erci. 2. Removal of the dGIs' activity which normally occurs during na tural flight reduced both the wingbeat frequency and flight duration, and increased the variability of the wingbeat frequency (Fig. 6). Intr acellular rhythmic stimulation of a single dGI during flight increased the wingbeat frequency and the duration of flight (Figs. 7, 8). The w ind sensitivity of the dGIs was unchanged during flight compared with at rest (Fig. 2). A single short burst of spikes in a dGI had complex effects on the flight muscle recording but apparently did not reset th e flight rhythm (Fig. 9). These results suggest that the rhythmic acti vation of the dGIs during natural light participates in the control of the wingbeat frequency and the flight duration (Fig. 12). 3. In contr ast to the dGIs, the vGIs became significantly less sensitive to wind during flight (Fig. 3). Stimulation of one of the vGIs (GI1) with 10 s pikes at roughly 180/s during flight evokes immediate cessation of fli ght (Figs. 10, 11). Given that the vGI activity can stop flight, the i nhibition imposed on the ventral group during flight appears to be des igned to prevent this group from interfering with the flight program ( Fig. 12).